U.S. patent application number 13/211884 was filed with the patent office on 2012-02-23 for deposition system with a rotating drum.
This patent application is currently assigned to VAECO INC.. Invention is credited to Richard DeVito.
Application Number | 20120045588 13/211884 |
Document ID | / |
Family ID | 45594290 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120045588 |
Kind Code |
A1 |
DeVito; Richard |
February 23, 2012 |
DEPOSITION SYSTEM WITH A ROTATING DRUM
Abstract
A deposition method comprises flowing a first gas into a
metallization zone maintained at a first pressure. A second gas
flows into a reaction zone maintained at a second pressure. The
second pressure is less than the first pressure. A rotating drum
includes at least one substrate mounted to a surface of the drum.
The surface alternately passes through the metallization zone and
passes through the reaction zone. A target is sputtered in the
metallization zone to create a film on the at least one substrate.
The film on the at least one substrate is reacted in the reaction
zone.
Inventors: |
DeVito; Richard; (Jamaica
Plain, MA) |
Assignee: |
VAECO INC.
Jamaica Plain
MA
|
Family ID: |
45594290 |
Appl. No.: |
13/211884 |
Filed: |
August 17, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61376181 |
Aug 23, 2010 |
|
|
|
Current U.S.
Class: |
427/475 ;
118/715; 118/720; 118/723R; 427/255.28; 427/569 |
Current CPC
Class: |
H01J 37/32779 20130101;
C23C 14/35 20130101; H01J 37/32899 20130101; C23C 14/345 20130101;
H01J 37/32816 20130101; C23C 14/0068 20130101; H01J 37/3476
20130101; H01J 37/3405 20130101; C23C 14/505 20130101; H01J
37/32458 20130101; C23C 14/042 20130101; C23C 14/0078 20130101;
C23C 14/0042 20130101; C23C 14/541 20130101; C23C 14/0089
20130101 |
Class at
Publication: |
427/475 ;
427/255.28; 427/569; 118/723.R; 118/720; 118/715 |
International
Class: |
C23C 14/35 20060101
C23C014/35; C23C 14/14 20060101 C23C014/14; C23C 14/04 20060101
C23C014/04; C23C 14/34 20060101 C23C014/34 |
Claims
1. A method for deposition comprising: flowing a first gas into a
metallization zone maintained at a first pressure; flowing a second
gas into a reaction zone maintained at a second pressure, the
second pressure being less than the first pressure; rotating a drum
including at least one substrate mounted to a surface of the drum,
the surface alternately passing through the metallization zone and
passing through the reaction zone; sputtering a target in the
metallization zone to create a film on the at least one substrate;
and reacting the film on the at least one substrate in the reaction
zone.
2. The method of claim 1 further comprising cooling the drum with a
liquid and applying an electrical bias to the drum to enhance
activation of the metal deposited on the at least one
substrate.
3. The method of claim 1 wherein sputtering includes substantially
shielding the anode from the first gas with the target.
4. The method of claim 1 wherein sputtering includes forming a wave
front parallel to a surface of the at least one substrate with a
mask interposed between the target and the at least one
substrate.
5. The method of claim 1 further comprising flowing the first gas
into a second metallization zone maintained at the first pressure,
sputtering a second target in the second metallization zone to
create a second film on the at least one substrate and rotating the
drum further comprising the surface passing through the second
metallization zone for each time the surface passes through the
reaction zone.
6. The method of claim 1 wherein pumping the reaction zone further
comprises encasing the reaction zone in an enclosure with a
differential pump, the differential pump maintaining the reaction
zone at the second pressure.
7. The method of claim 6 wherein the differential pump pumps the
metallization zone to the first pressure and another reaction zone
pump pumps the reaction zone to the second pressure.
8. The method of claim 1 further comprising neutralizing a charge
of the second gas by injecting electrons into the reaction
zone.
9. The method of claim 1 wherein the second gas is replaced with
another reactive gas after a number of rotations of the drum.
10. A deposition system comprising: a metallization zone including
a sputtering system for depositing a film on the at least one
substrate sputtered from a target and pressurized with a first gas
at a first pressure; a reaction zone including an ionization source
and pressurized with a second gas at a second pressure, the second
pressure being less than the first pressure; and a drum configured
to hold at least one substrate mounted to a surface of the drum,
upon rotation of the drum the surface alternately passing through
the metallization zone and passing through the reaction zone, the
metallization zone proximate to a first location of the drum, the
reaction zone proximate to a second location of the drum, and the
distance along a circumference of the drum from the first location
to the second location exceeding a mean free path of the second
gas.
11. The system of claim 10 wherein the drum is cooled with a liquid
and is in communication with an electrical bias to enhance
activation of the metal deposited one the at least one
substrate.
12. The system of claim 10 wherein the sputtering system comprises
a target interposed between an anode and the first gas, the anode
substantially isolated from the first gas by the target.
13. The system of claim 10 wherein the sputtering system comprises
a mask interposed between the target and the at least one
substrate, the mask configured to form a wave front of a sputtered
material parallel to a surface of the at least one substrate.
14. The system of claim 10 further comprising a second
metallization zone proximate to a third location of the rotating
drum, the second metallization zone including a second sputtering
system for depositing a second metal on the at least one substrate
and pressurized with the first gas at the first pressure.
15. The system of claim 10 wherein the sputtering system includes a
magnetron with a length substantially equal to a height of the
rotating drum plus twice a width of the target wherein the length
is collinear with the height and the length is perpendicular to the
width.
16. The system of claim 10 wherein the ionization source is a
linear ion source.
17. The system of claim 10 wherein the reaction zone is interposed
between a pair of inner baffles, the inner baffles are interposed
between a pair of differential pumps, the differential pumps are
interposed between a pair of outer baffles, an inner space between
the inner baffles and the rotating drum an outer space between the
outer baffles and the rotating drum and a speed of the differential
pumps are arranged to maintain a differential pressure between the
inner baffles and the outer baffles less than the second pressure
in the reaction zone.
18. The system of claim 10 wherein the reaction zone includes an
electron source configured to neutralize a charge of the second
gas.
19. The system of claim 10 wherein the reaction zone is configured
to switch the second gas with another reactive gas after a number
of rotations of the drum.
20. A deposition system comprising: a metallization zone including
a sputtering system for depositing a film on the at least one
substrate sputtered from a target and pressurized with a first gas
at a first pressure; a reaction zone including an ionization source
and pressurized with a second gas at a second pressure, the second
pressure being less than the first pressure, the reaction zone
interposed between a pair of inner baffles and including a reaction
zone pump, the inner baffles interposed between a pair of
differential pumps, the differential pumps interposed between a
pair of outer baffles, the reaction zone pump configured to pump
the reaction zone to the second pressure and the pair of
differential pumps configured to assist a main chamber pump to pump
the metallization zone to the first pressure, the main chamber pump
in communication with the metallization zone and the reaction zone;
and a drum configured to hold at least one substrate mounted to a
surface of the drum, upon rotation of the drum the surface
alternately passing through the metallization zone and passing
through the reaction zone, the metallization zone proximate to a
first location of the drum, the reaction zone proximate to a second
location of the drum, and the distance along the circumference of
the drum from the first location to the second location exceeding a
mean free path of the second gas.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a utility application claiming priority
to co-pending U.S. Provisional Application Ser. No. 61/376,181
filed on Aug. 23, 2010 entitled "A METHOD TO DEPOSIT REACTIVE FILMS
ON A ROTATING CYLINDER," the entirety of which is incorporated by
reference herein.
FIELD OF THE INVENTION
[0002] The invention relates generally to a thin film deposition
system. More specifically, the invention relates to a deposition
system with separate metallization and reaction zones for
deposition of reactive films.
BACKGROUND
[0003] DC Magnetron Sputtering is a thin film deposition technique.
For example, sputtering can occur in an environment containing
Argon gas (Ar). A negative DC potential is applied to a conductive
metal "target." A plasma discharge is established to ionize the gas
thereby creating Ar+ ions. The positively charged Ar+ ions
accelerate towards the negatively charged target and causes
ejection of the target through sputtering, which in turn creates a
metal film on an opposing placed substrate.
[0004] Introduction of reactive gases such as O.sub.2 or N.sub.2
can cause the film to take on properties of the compounds created
by the reaction of these gases with the deposited metal film.
Further ionization and acceleration of these reactive gases can
enhance the reactivity between the gas and the film in addition to
improving the density of the film as well as influence other film
properties such the film stress, hardness, index and absorption.
Conventional deposition systems are complex and suffer from issues
including reduced wafer throughput and material contamination
issues, which limits film quality and requires extended
preventative maintenance cleaning of the deposition equipment. This
effects over all cost of ownership
BRIEF SUMMARY
[0005] In one aspect, the invention features a method for
deposition comprising flowing a first gas into a metallization zone
maintained at a first pressure. A second gas flows into a reaction
zone maintained at a second pressure. The second pressure is less
than the first pressure. A rotating drum includes at least one
substrate mounted to a surface of the drum. The surface alternately
passes through the metallization zone and passes through the
reaction zone. A target is sputtered in the metallization zone to
create a film on the at least one substrate. The film on the at
least one substrate is reacted in the reaction zone.
[0006] In another aspect, the invention features a deposition
system comprising a metallization zone including a sputtering
system for depositing a film on the at least one substrate
sputtered from a target and pressurized with a first gas at a first
pressure. A reaction includes an ionization source and is
pressurized with a second gas at a second pressure. The second
pressure is less than the first pressure. A drum is configured to
hold at least one substrate mounted to a surface of the drum. Upon
rotation of the drum the surface alternately passes through the
metallization zone and passes through the reaction zone. The
metallization zone is proximate to a first location of the drum.
The reaction zone is proximate to a second location of the drum.
The distance along a circumference of the drum from the first
location to the second location exceeds a mean free path of the
second gas.
[0007] In another aspect, the invention features a deposition
system comprising a metallization zone including a sputtering
system for depositing a film on the at least one substrate
sputtered from a target and pressurized with a first gas at a first
pressure. A reaction zone includes an ionization source and is
pressurized with a second gas at a second pressure. The second
pressure is less than the first pressure. The reaction zone is
interposed between a pair of inner baffles and includes a reaction
zone pump. The inner baffles are interposed between a pair of
differential pumps. The differential pumps are interposed between a
pair of outer baffles. The reaction zone pump is configured to pump
the reaction zone to the second pressure. The pair of differential
pumps is configured to assist a main chamber pump to pump the
metallization zone to the first pressure, the main chamber pump is
in communication with the metallization zone and the reaction zone.
A drum is configured to hold at least one substrate mounted to a
surface of the drum. Upon rotation of the drum the surface
alternately passes through the metallization zone and passes
through the reaction zone. The metallization zone is proximate to a
first location of the drum. The reaction zone is proximate to a
second location of the drum. The distance along a circumference of
the drum from the first location to the second location exceeds a
mean free path of the second gas.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0008] The above and further advantages of this invention may be
better understood by referring to the following description in
conjunction with the accompanying drawings, in which like numerals
indicate like structural elements and features in various figures.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention.
[0009] FIG. 1 is schematic top view of an embodiment of a
deposition system according to the invention.
[0010] FIG. 2 is partial cross-sectional view of the deposition
system shown in FIG. 1.
[0011] FIG. 3 is perspective view of an embodiment of a drum usable
with the deposition system in FIG. 1
[0012] FIG. 4 is a schematic view of an embodiment of a
metallization zone usable with the deposition system in FIG. 1
[0013] FIG. 5 is a schematic view of an embodiment of a sputtering
mask positioned relative to two substrates.
[0014] FIG. 6A is a perspective view of an embodiment of a
deposition system.
[0015] FIG. 6B is a perspective view of an embodiment of a reaction
zone usable with the deposition system in FIG. 6A.
[0016] FIG. 7A is a perspective view of an embodiment of a
deposition system.
[0017] FIG. 7B is a perspective view of an embodiment of a reaction
zone usable with the deposition system in FIG. 7A.
[0018] FIG. 8A is a schematic view of an embodiment of a
metallization zone usable with the deposition system in FIG.
7A.
[0019] FIG. 8B is a schematic view of an embodiment of the
metallization zone.
[0020] FIG. 8C is a schematic view of an embodiment of the
metallization zone with an aperture formed by an aperture
shield.
DETAILED DESCRIPTION
[0021] Embodiments of deposition systems described herein provide
for deposition of metallic films and their subsequent reaction with
improved throughput and quality over conventional systems. For
example, and without limitation, an aluminum film is deposited on a
silicon wafer and then subsequently reacted with oxygen to form
Al.sub.2O.sub.3 as a dielectric in a semiconductor component. Other
example films are SiO.sub.2, TiN and TiC. In other examples,
multiple metallic film layers are deposited, each with a different
index of refraction to produce a high quality optical coating. In
another example, multiple reactive gases are alternately used to
form SiOxNx materials. In another example, multiple metallic
targets are used with an inert gas in the reaction zone to form
precise multilayer films for X-ray mirrors. Many combinations of
metal films and reactive gases are usable with the embodiments
described herein in an efficient manner with less cross
contamination of materials and improved consistency of
deposition.
[0022] FIG. 1 shows a preferred embodiment 10 of a deposition
system in accordance with the invention. The embodiment 10 includes
an outer enclosure 12 with a separate metallization zone 14 and a
reaction zone 16. A drum 18 has a plurality of substrates 20
affixed to the outer surface of the drum 18 so that rotation of the
drum 18 causes at least one of the substrates 20 to alternately
pass through the metallization zone 14 and the reaction zone 16. In
other embodiments the drum 18 is replaced with a different shape
other than circular. For example, a hexagonal drum is used to
accommodate larger substrates. It is envisioned that other drum
shapes are used in other embodiments to accommodate substrates of
different size, thickness and shapes.
[0023] The metallization zone 14 includes a magnetron 22 fed by an
inert gas source 24. The magnetron 22 is enclosed in a vestibule 26
and has an aperture 27. The aperture allows pressure introduced
into the vestibule to build up to a pressure higher than in the
reaction zone. The inert gas source is preferably Argon but can
also be other inert gas such as Xenon for example. A pair of outer
baffles 28 are arranged to assist in the maintaining of the
pressure developed from the gas source 24 feeding an inert gas into
the metallization zone 14 and exiting through a pump (not visible
in FIG. 1). The baffles 28 extend close to the drum 18 while
maintaining separation from the substrates 20 as they rotate
through the metallization zone 20. The distance of the aperture
from the drum surface 18 also determines the pressure buildup in
the vestibule 26.
[0024] The reaction zone 16 includes an ion source 30 fed by a gas
source 32. The gas is preferably a reactive gas including but not
limited to Oxygen or Nitrogen but may also be an inert gas such as
Argon. In one embodiment, a hollow cathode electron source 42 is
used to inject electrons into the reaction zone 16 to maintain
plasma neutrality or a zero net charge of positively and negatively
charged ions in the reaction zone 16. A pair of inner baffles 38
and outer baffles 40 assist with maintaining the pressure in the
reaction zone 16 caused by the inflow of gas from the gas source 32
and exiting through a pair of differential pumps 36. The reaction
zone 16 is further enclosed by an enclosure 34 to assist with
maintaining the reaction zone pressure. In addition, the metal film
being deposited on the substrate 20 is itself an additional
selective pump of the reactive gas in the reaction zone. Both the
differential pumps 36 and the film itself act to reduce any
residual reactive gas to levels that cannot appreciably penetrate
into the higher pressure metallization zone 14. A final pumping
step is the subsequent selective pumping of any reactive gases that
enter the metallization zone 14 by the sputtered metal atoms and
are getter-reacted on the inner walls of 26. The low mean free path
of any O.sub.2 molecules, for example within the higher Argon
background pressure metallization zone 14 causes any O.sub.2 gas to
be reacted and gettered before contact with the target.
[0025] In one embodiment, the system 10 is pumped to a base
pressure P.sub.b and the metallization zone 14 is filled with Argon
gas, with the metallization zone 14 maintained at a pressure Pa,
1.times.10.sup.-3 to 1.times.10.sup.-2 Torr for example. A reactive
gas such as O.sub.2 is flowed into the reaction zone 16 through
source 32 and maintained at a pressure Pr, where Pr is
substantially less than Pa, 1.times.10.sup.-4 to 5.times.10.sup.-4
for example. The Argon gas is positively charged in the
metallization zone 14 with the magnetron 22 by igniting a plasma
discharge with a direct current (DC), pulsed or radio frequency
(RF) power supply. The positively charged Argon ions strike a metal
target mounted on the magnetron 22 resulting in sputtering of a
metal film on the substrate 20 as it passes through the
metallization zone 14. The substrate 20 then passes through the
reaction zone 16 upon rotation of the drum 18. The reactive gas is
ionized into a plasma with the ion source 30. In one embodiment the
ion source is an electron cyclotron resonance (ECR) plasma source.
The substrate 20 with the deposited metal film is then reacted and
densified in the reaction zone 16. For example, an aluminum film
would be converted to Al.sub.2O.sub.3 if O.sub.2 were the reactive
gas in the reaction zone 16 and aluminum were the target used in
the metallization zone 14. The ion source 30 should be understood
to include any plasma or ion source suitable to activate the
reactive gas or species (e.g. O.sub.2) and accelerate into the
substrate 20 to cause a substantially complete reaction between the
reactive gas and the deposited metal to form a stoichometric film
or alloy and to densify the film. FIG. 2 further illustrates the
system described in FIG. 1. The pump, a cryogenic pump for example,
52 is used to discharge the Argon used in the metallization zone 14
and in part the reactive gas used in the reaction zone 16. The
reaction gas is discharged through a combination of pump 52 and the
differential pumps 36 controlled in part by the spacing of the
baffles 38 and 40 relative to the rotating drum 18.
[0026] In one example, the system 10 is operated by rotating the
drum 18 at a fixed speed. A reactive gas is set to a pressure Pr
and the ion source is ignited. The energy and flux of the ion
source is adjusted for the required reaction. Argon gas is flowed
into the metallization zone 14 and the flow of Argon is adjusted to
a pressure Pa. The magnetron 22 is then ignited to form a plasma
and the power to the magnetron 22 is adjusted to a power P such
that 5-7 Angstroms (A) of metal film are deposited on a substrate
20 for each revolution of the drum 18. The substrate 20 is then
passed through the reaction zone to react the deposited film and
then the drum subsequently passes the substrate back to the
metallization zone 14 to deposit another metal film. With this
method, the film growth is rapid, stable and predictable due to the
linear relationship of magnetron power to metal film deposition
rate. As the target in the magnetron 22 erodes predictably and the
deposition rate drops, the operator of the system 10 increases the
power to the magnetron 22 to maintain a substantially constant
deposition rate. In one example, this adjustment of magnetron power
is controlled automatically by an algorithm based on the time the
system 10 has been in operation.
[0027] For example, if 5 A (e.g. 5.times.10.degree. m) are
deposited for each revolution of the drum 18, at a drum revolution
of 100 rpm, one will deposit 500 A of reacted film in one minute
and 5000 A in ten minutes. The rate of deposition is further
limited by the reaction time of the reactive gas, which is further
limited by the maximum ion flux or beam current that can be
delivered by the ion source 30.
[0028] A further example of settings used in the system 10 uses a
cathode measuring three inches by six inches (the cathode being
part of the magnetron 22 described below) and 900 watts of DC power
applied to the magnetron 22, which produces a deposition rate of 32
A of aluminum for each second that the substrate is in the
metallization zone. This is referred to as the "static" deposition
rate. For a drum 18 rotating at 60 rpm, a "dynamic" deposition rate
of 1.15 A/rev. is produced for a typical metallization zone and
substrate. If the magnetron 22 power is increased to 1500 watts the
static deposition rate would be approximately 1.66 greater than the
rate using 900 watts resulting in a 53 A/sec static deposition
rate. In one example of system 10 a dynamic rate of 5 A/rev. of
aluminum is deposited using 3.6 kW of magnetron power and a drum 18
rotation rate of 60 rpm. A reactive flux of oxygen O.sub.2.sup.+
must be maintained at a sufficient magnitude to convert the
deposited aluminum film to a stoichiometric Al.sub.2O.sub.3 film
for pass of the substrate 20 through the reaction zone 16.
According to the molecular formula for Al.sub.2O.sub.3 50% more
O.sub.2.sup.+ ions are required than aluminum to completely react
the film. For example, a metal deposition rate of 5 A/rev. is
equivalent to a metal flux of 3.times.10.sup.15 atoms/cm.sup.2/sec.
at a drum 18 revolution rate of 60 rpm. An O.sub.2 ionized flux of
similar magnitude with an average energy of approximately 30-60
eV/atom is used to react the film to produce Al.sub.2O.sub.3. It is
important not to exceed an upper limit of the eV/atom energy by too
much, because re-sputtering of the deposited film will interfere
with the deposition process. In addition, beyond this energetic
threshold the energetic ions can re-sputter portions of the film
causing non-stoichiometric films or implant into the film thereby
causing localized stress defects. This upper limit is determined by
the specific film being deposited.
[0029] Because the reactive time in the reaction zone 16 is limited
by the ion current or flux, it is important that the ion source 30
be as close to the substrate 20 as possible. With a linear ion
source is it possible to get much closer to the substrate 20 than
to arrange a series of circular sources along the height of the
drum 18. If a circular ion source is used, the arrangement of the
sources must be raised above the substrate so that the ion source
height and separation from the substrate 20 gives a flux
distribution, (which is the sum of the individual sources) being
uniform across the substrate. For example, for a drum 18 that is
approximately three feet in height, the ion sources should be 5-8
inches above the substrate. This close proximity is not possible
with multiple circular sources due to beam superposition issues. In
contrast, the magnetron 22 does not have to be in such close
proximity to the substrate 20 because the magnetron 22 can support
large power densities.
[0030] The close proximity of the ion source 30 to the substrate 20
and the baffles 38 and 40 to the drum 18 can limit the substrate 20
thickness and curvature. In this case, the drum 18 can have a
retro-machined or recessed surface within which the substrate 20 is
held. FIG. 3 shows a drum 18 with a retro-machined surface for each
substrate 20. In one example, the top of the substrate 20 is
"proud" (e.g. flush) to the surface of the drum 18. Further
variations to the drum shape are considered within the scope of the
invention, including replacing the substrate with another object to
receive a metal film.
[0031] Uniformity and stress of film deposition is further enhanced
by adjusting the pressure Pa in the metallization zone 14 and the
target to substrate 20 distance or the pressure-distance product
(PxTsd). Adjusting Tsd is facilitated by mounting the magnetron 22
within a flanged housing with adjustment rods 72 as shown in FIG.
4. Adjusting the pusher rods 72 moves the magnetron 22 closer to
the substrate 20 mounted on the drum 18. In a preferred embodiment,
the magnetron 22 includes a mask 82 between a target 78 and the
substrate 20. An anode 76 is disposed between the target 78 and a
cathode 74 and is designed to have a small annular portion between
the target 78 and the substrate 20. In one example, the anode is
biased to a ground potential and the cathode 74, which electrically
communicates with the target 78 is biased to a negative potential
less than ground. The positively charged inert molecules (e.g. Ar+)
will accelerate towards the negatively charged target 78 and impact
the target resulting in sputtering.
[0032] To achieve optimum uniformity of deposited material on the
substrate 20 using a linear magnetron, the magnetron length should
be substantially equal to the drum 18 height plus twice the target
width. For example if the drum 18 is one meter in height and the
magnetron is 10 cm. wide, the magnetron length should be
approximately 1.2 meters. In one example, gas lines to and from the
gas source 24 and supplying the magnetron 22 are chosen to
substantially eliminate a pressure gradient along the magnetron
length so enhance film linear uniformity.
[0033] In a preferred embodiment, a mask 82 as shown in FIG. 5 is
used to enhance deposition uniformity. The mask 82 is interposed
between the magnetron 22 and the substrate 20 and is shaped to
account for local film variations. For a flat substrate 20 the mask
82 produces a linear wave front of sputtered material to the
substrate 20. Various alterations to the mask are used to shape the
wave front to match the surface of non-planar substrates, for
example a convexed or concaved substrate. FIG. 5 further
illustrates the positioning of the mask 82 relative to a substrate
20a that has just exited the metallization zone 14 and a substrate
20b that is within the metallization zone 14. The deposited metal
film uniformity primarily determines the reacted film uniformity.
This is because the ion source 30 is typically operated in the
saturation mode. In other words, slightly more current is delivered
to the ion source 30 than is needed to cause saturation of the film
stoichiometry. For example, if the voltage of the ionized reactive
gas is kept sufficiently low (e.g. less than 100-125 eV) the
deposited reacted film's molecular bonds will not be broken and
stoichiometry is maintained in the reacted film. Once stoichiometry
is reached, the film is stable. In an embodiment where the system
10 is configured to make alloys, the ion source 30 is operated at a
setting between zero energetics and less than saturation to obtain
a film of any composition.
[0034] In one embodiment, the rotating drum 18 is cooled with a
liquid, for example water and has an RF, DC or pulsed electrical
bias applied to enhance activation or assist through re-sputtering
in the planarization of a substrate with photolithographic
features. The linear magnetron 22 in the present invention easily
lends itself to a hidden anode 76 design as shown in FIG. 4. In
prior solutions using reactive sputtering, the anode is also the
substrate and becomes coated with an insulator. The electrons in
the plasma can therefore no longer return to ground, and an
accumulation of charges causes the plasma to spread out to the
substrate seeking a return path to ground. The magnetron plasma now
is in contact with the substrate, which results in undesirable
substrate heating. A hidden anode 76 as shown in FIG. 4 overcomes
this problem because the anode will not be coated with an insulator
and this in turn keeps the plasma confined to the target 78 thereby
reducing the substrate heating.
[0035] In prior solutions, the magnetron 22 is purposely operated
in an unbalanced mode. In this mode the plasma is made to extend to
the substrate 20 thereby adding an ion assist to the substrate from
the Argon ions in the magnetron plasma. This plasma extension
provides for film and gas reactivity however it is combined with
the metallization zone. In this unbalanced configuration, a high
power and high film deposition rate will put severe constraints on
the substrate temperature and corresponding cooling requirements.
Unlike the prior solutions, the present invention separates the
metallization zone 14 and the reaction zone 16 in an effective
manner.
[0036] In a preferred embodiment, the substrates 20 are mounted
vertically as shown in FIG. 3 and a linear magnetron 22 is now used
for film deposition. Every point on a vertical line of the
substrate spend the same time under the deposition flux while in
the metallization zone 14 thus substantially eliminating the center
to edge film thickness variation or gradient along the substrate
20. Prior solutions that are encumbered by this film gradient are
required to use a delta-shaped magnetron to produce uniform films
at added expense and system complexity. Even with the delta-shaped
magnetron, a mask is still required to enhance uniformity. In the
present invention, no such gradient exists, thereby allowing use of
a standard linear magnetron with standard targets.
[0037] Due to the complete separation between the metallization
zone 14 and the reaction zone 16, the system 10 operates in an
open-loop with little dependency between the zones and without the
risk of reactive sputter hysteresis which "poisons" or oxidized the
metal target 78 and consequently shuts down the sputtering process.
Furthermore separation of the zones avoids the requirement to use
pulsed sputtering or other devices to reduce arc events due to
target poisoning although in one example pulse sputtering is used
to enhance ionization at the target for effecting film properties.
Separation of the metallization zone 14 and the reaction zone 16
and consequently the reduction in target poisoning, requires a
pressure differential between the zones of approximately one order
of magnitude and a physical separation greater than the mean free
path of the reactive gas. In one example, the metallization zone 14
has a pressure Pa of 1.times.10.sup.-3 torr while the reaction zone
16 has a pressure Pr of 1.times.10.sup.-4 torr. This pressure
differential and mean free path difference provides a diffusive gas
barrier to further enhance the isolation of the two zones. It is
envisioned that a greater distance between the two zones will also
permit a reduction in the pressure differential and that various
combinations of pressure differential and physical separation are
within the scope of the invention. The present invention overcomes
limitations of previous solutions that required complicated
feedback loops involving optical plasma spectroscopy or mass flow
controller feedback loops to control gas flow and the magnetron
power supply.
[0038] The present invention also overcomes limitations in previous
solutions that require the cathode of the magnetron to be encased
in a differentially pumped enclosure rather than just enclosing the
reaction zone 16 in a differentially pumped enclosure.
Advantageously, the present approach facilitates a system with
multiple metallization zones because only the common reaction zone
16 is differentially pumped as shown in FIGS. 6A and 6B. In FIG. 6A
a system 90 has an enclosure 12 with an opening 92 for the ion
source 30. The reaction zone 16 is encased in an enclosure 34 and
is differentially pumped with pumps 36. In FIG. 6B, the enclosure
34 includes a pair of inner baffles 38 and a pair of outer baffles
40. The differential pumps 36 are positioned outside of the inner
baffles 38 and inside of the outer baffles 40. The reaction zone 16
is within the inner baffles 38.
[0039] The pumps 36 and the baffles 38 and 40 are chosen so that
the pressure outside of the reaction zone 16, (between the reaction
zone 16 and the metallization zone 14) is reduced to a pressure
substantially less than the reaction zone 16, 1.times.10.sup.-5
torr for example. In this case if the pressure outside of the
reaction zone is Pr and the conductance of the baffles is Cb
(measured in torr-litres/sec) and the reduced pressure outside the
enclosure 34 is Po then the speed of the pumps 36 is calculated by
the equation Spump=(Pr-Po)/Cb. By enclosing the reaction zone 16
and differentially pumping this zone separately from the rest of
the system, pump sizes and system size are reduced, allowing the
target and ion source to be more loosely coupled.
[0040] In one of the preferred embodiments the reaction zone 16
includes an additional pump 112 positioned between the inner
baffles 38 as shown in FIGS. 7A and 7B. With the addition of pump
112, the baffles 38 and 40 can be moved closer to the drum 18 for
improved isolation of the reactive gases from the rest of the
system. In another embodiment, the pair of inner baffles 38 is
moved closer to the drum 18 and the pair of outer baffles 40 are
moved further away from the drum 18 such that the differential
pumps 36 providing differential reduction of the reactive gas can
now be used to also pump the inert gas from the metallization zone
thereby eliminating the need for pump 52 shown in FIG. 2. The speed
of the pump 112 is limited by the conductance of the aperture
crated by the outer baffles 40 and the speed of the pump 112.
[0041] With the improved isolation of the reactive gases as shown
in FIGS. 7A and 7B, the linear magnetron 22 can be positioned
further from the substrate 20 as shown in FIG. 8A. Advantageously,
this further reduces particles on the substrate 20. Because the
inert gas is introduced within the magnetron 22 locally, then the
open area through which the inert gas is pumped is effectively a
sputter aperture with conductance Ca.
[0042] FIG. 8B shows an embodiment of the metallization zone 14
where the plasma from the magnetron 22 is substantially confined by
a pair of inner baffles 142. FIG. 8C shows one of the preferred
embodiments of the metallization zone 14 where the plasma is
confined by an aperture 27 formed by an aperture shield 26. If the
pressure in this sputter vestibule 26 is fixed at pressure Pa and
assuming the main pump 52 speed is much higher than the speed of
the differential pumps 36 and the main pump 52 has a speed
P.sub.speed, then the size of the aperture can then be calculated
to maintain P.sub.a. The distance of the aperture plate from the
substrate holder (e.g. drum) 18 also contributes to the pressure
build up in the vestibule 26.
[0043] The vertical orientation of the deposition in the
metallization zone 14 advantageously reduces the susceptibility of
particles landing on the substrate 20. Unlike prior solutions that
used downward facing deposition the requirement for shutting down
the system for maintenance is reduced and the use of full-face
erosion targets to minimize target re-deposition is eliminated.
Delta magnetrons as used in the prior solutions have a long
meandering non-sputtered zone, which becomes saturated with
re-deposited film. This film will over time "spall" off due to
stress, which greatly contributes to undesirable particles reaching
the substrate 20. By using a linear magnetron 22 whose
re-deposition area is substantially less than a delta magnetron,
particles are reduced in thick coatings.
[0044] A further advantage of the system 10 with monolayer
deposition, and high speed passing through the zone with inert gas
and subsequent conversion to a dense stoichometric reacted layer is
the significant reduction of the inert gas in the substrate 20. By
reducing the inert gas (e.g. Argon) in the substrate 20, defect
induced stress variation is greatly reduced. The reacted film
stress is then controlled by film densification with a process
known as atomic penning due to the ion source. The stress control
is achieved by controlling the atom/ion ratio (e.g. metal atom flux
to ion flux ratio) and momentum exchange of the ion at the surface.
By controlling magnetron 22 power, anode 76 current and anode 76
voltage the film stress can be varied or controlled or
alternatively, magnetron 22 power, anode 76 current and anode 76
voltage can be held constant and the atom/ion ration and metal rate
per revolution of the drum 18 is controllable by varying the drum
18 rotation speed.
[0045] In one embodiment a second magnetron is added to the system
10 to form high and low index metal oxide layers on a substrate 20
to produce high quality optical coatings. For example, a Silicon
target in one magnetron and a Tantalum target in a second magnetron
provides are any number of SiO.sub.2/Ta.sub.2O.sub.5 optical
coatings including anti-reflection, band bass and blocking
coatings. The formation of the optimal layers is easily monitored
by a gated optical monitor. Other embodiments use more than two
magnetrons to provide even more complex structures. In another
embodiment, two magnetrons are used each with their own metal
target and the reactive gas in the reaction zone 16 is replaced
with Argon to rapidly form precise metal multilayer films from low
Z materials for X-ray mirrors.
[0046] In another embodiment for multilayer coatings, an additional
(e.g. second or more) magnetron is mounted within a single attached
vestibule 26. The additional magnetron is used and indexed with a
motor controller. In this way a layer A is deposited with magnetron
A then halted and magnetron B is then rotated in position in front
of the aperture, power is applied to magnetron B and a film B is
deposited. This embodiment of a multiple target sputtering system
greatly reduces machine foot print and cost of ownership.
[0047] In another embodiment, the gas source 32 is pulsed or
alternated between different gases to form different combinations
of films. For example, a Silicon target is used, with O.sub.2 and
N.sub.2 reactive gases used sequentially to produce SiN and
SiO.sub.2 layers. Alternatively, an O.sub.2/N.sub.2 mixture is used
to form SiONx materials.
[0048] While the invention has been shown and described with
reference to specific preferred embodiments, it should be
understood by those skilled in the art that various changes in form
and detail may be made therein without departing from the spirit
and scope of the invention as defined by the following claims.
* * * * *